In the prior art, a lapping machine as shown in FIG. 1 is used for lapping workpieces such as silicon wafers, synthetic quartz glass, rock crystal, liquid crystal glass, and ceramics. The machine of FIG. 1 includes a lower lapping plate 1 made of spheroidal-graphite cast iron. The plate 1 is coupled for rotation to a drive (not shown). On the inner diameter side of the plate, a sun gear 2 is disposed at the center. An annular or internal gear 3 is disposed along the outer periphery of the plate 1. A plurality of carriers 4 are disposed in mesh engagement with the gears 2 and 3. Each carrier 4 is provided with workpiece-holding holes 5. A workpiece 6 is fitted within each holding hole 5. Above the carriers 4, an upper lapping plate may be disposed for rotation like the lower lapping plate 1, though not shown. When the plate 1 is rotated, the carriers 4 are rotated counter to the plate rotation. Then, the workpieces 6 are lapped with loose abrasive grains fed to the plate as the workpieces revolve about the gear 2 and rotate about their own axes.
As polishing and lapping steps are repeated using the lapping machine described above, the plate is worn to assume a convex or irregular shape. Once the plate is worn to such a shape, a plate-dressing jig made of the same cast iron material as the plate is used to true the plate surface for flatness while loose abrasive grains are fed thereto. After the plate is dressed in this way, it can be used again to repeat polishing and lapping steps in a similar manner. Known plate-dressing jigs used in the art for dressing the surface accuracy of the plate of the lapping machine for carrying out polishing and lapping steps include those described in JP-A 2000-135666 and JP-A 2000-218521.
Although these plate-dressing jigs are effective for dressing the lapping plates for flatness, they are ineffective in increasing the efficiency of lapping operation. It would be desirable to have a method of carrying out more efficient lapping operation.